New ultraviolet absorption cross-sections of BrO at atmospheric temperatures measured by time-windowing Fourier transform spectroscopy

Abstract

The UV absorption cross-section spectra of the atmospherically important radical BrO have been determined using the recently developed technique of time-windowing Fourier transform spectroscopy (TW-FTS). The absorption spectra of the A2Π3/2–X2Π3/2 band system were recorded in the flash photolysis of a gaseous mixture of Br2 and O3. The bromine-photosensitized decomposition of O3 was observed at five different temperatures between 203 and 298K. The absolute UV absorption cross-section was determined from the time-dependent observation of reactant and product absorptions and by a kinetic analysis of the BrO behavior. The integrated UV absorption cross-section of BrO was, within the accuracy of the measurements, constant over the temperature range studied, as expected from spectroscopic considerations. For the (7, 0) vibrational band at 29540cm−1 (338.5nm), the peak absorption cross-sections were determined to be 2.19±0.23 at 298K, 2.23±0.23 at 273K, 2.52±0.26 at 243K, 2.75±0.29 at 223K, and 3.03±0.31 at 203K (all in units ×10−17cm2permolecule, at a spectral resolution of 3.8cm−1, with error intervals of 2σ). Further, vibrational constants and the dissociation limit for the electronic state A2Π3/2 were derived. The A←X dissociation energy was determined to be D0=35240±160cm−1 or 421.6±1.9kJ/mol.